Laminated SIPs?

[captainsam]

OK,

Here’s a thought about how to vacuum bag a large panel. I have seen the vacuum bagging process up close in the composite aircraft part repair business but I am not particularly experienced in the area.

Mark,

I have considered vacuum bagging and am really leaning that way right now. A shop vacuum won't do the job however. We need between 5-7 psi pressure so a shop vac is not enough. It would be useful to quickly evacuate the bag before the real deep vacuum is intoduced. I have found the vacuum pumps, fittings, hoses, sealing tape, and bagging film really are not that expensive. I think it can all be done for $ 250 with some scrounging.

I would first build a flat surface table or frame large enough for the panel to fit on it with the table extending 3-4 inches extra all around. On the edges I would lay a wood framework around the circumference equivalent in thickness to the panel being built up.

It seems to me that the framework you describe might have to be completely against the panel edge or the 5-7 psi pressure would try to collapse the frame inward. A 4 " high frame 8' long would have almost a ton of force evenly pressing against it.

This dimension is not critical, as a frame of this design would allow panels of varying thicknesses to be manufactured (within reason). All the joints and fasteners must be sealed with glue, calking or sealing tape so that the frame is airtight. Now you drill a hole through the edge of the frame and glue and seal in a tube or hose that can be adapted to your vacuum.

Why couldn't I lay a sheet of 6 mil polyethelene film on the table, lay up the panel on the sheet, install a vacuum cup assembly, fold the sheet over the top, seal with a Constant heat Roller all around the item.

To build a panel lay your substrate in the frame, apply a coat of waterproof flooring adhesive

While this adhesive may or may not be sufficient, I'm sold on the one part water activated polyurethane adhesive the commercial panel builders use. It is proven to work. It is the same formula as Gorilla Glue.. and several others.

If all this sounds like too much effort then I like the idea of building a 2x6 frame skinned with plywood and a ramp at one end. You lay-up your panel in the driveway, set the frame on top and park your car on it overnight.

I thought of this but you may need a big car..or truck. To exert a 5 psi pressure on a 4' X 8' panel you would need a car that weighs 23,040 lbs. ( 32,256 lbs. for a 7 psi push). The problem is, how do you carry that force from the wheels evenly to the the entire surface of the panel. In reality, the tires would collapse the panel and foam under them. This is why panel presses are so large and heavy. It takes an incredibly strong. reinforced steel panel to take such a high load from a hydraulic piston and distribute it over a large area without bending ( or deflection). Even floor joists in a house are designed to deflect up to 1/240th or 1/360th of their length. For a 4 foot wide panel 1/360th is over 1/8th inch. Now. using the house floor idea, imagine removing the joists and just put the load on the subfloor. The beauty of bagging is that the pressure is perfectly even across the whole panel...quite a feat considering the hardware it takes to do it on a commercial SIP press. The press below is a bargain at only $30,000.... about the cheapest in the market by over half.


I have considered a few alternatives to a panel press or vacuum bagging :

1) The impractical vehicle idea we just discussed.

2) A pool filled with water over the panel, fill it, and viola!

But to exert even 5 psi takes a pool with a depth of 138.4 inches ( over 11.5 feet).

3) Placing concrete blocks on the entire panel surface.

Now 5 psi is 720 (5 X 144) pounds per square foot. Concrete weighs about 150 lbs. per cubic foot. To produce a 720 force, each 12" X 12" block would have to be 4.8 feet high. I guess you could cast a 4' X 8' block of concrete that is 4.8 feet high and set it on the panel you are making with a strong forklift... but this seems impractical too.

4) While in Home Depot I saw a high stack of Drywall and thought: A 4' X 8' pile of weight perfectly distributed to provide pressure. You could load the panel a couple sheets at a time so no forklift needed.

But 5/8" sheetrock weighs 2.2 lbs. per sq. ft. To get 720 lbs requires a stack of 327 sheets of drywall. That's a stack 204 inches( over 17 feet) high. Scratch that idea.

5) The only idea that I have had so far that "might" work is by using Dunnage Bags. These are very large thin air bladders that trucking companies use to exert low pressures against truck loads filling voids to keep them from shifting. They come in sizes larger than 4' x8' panels. Now I know some of you are already smiling but I'll continue for the rest of you. Now if a way could be designed to use such a bag to push against a SIP it would exert absolutely even pressure... since the pressure anywhere in a inflated bag must be constant. As long a surface contact could be maintained with the panel face, the pressure would be constant. The bags are designed for up to 8 psi ( 28 psi is the designed failure pressure). They are made of vinyl (only to about 3 psi), and paper and polypropylene (up to 8 psi). Now imagine a frame to hold the bag and withhold the pressure exerted by the bag. See the diagram below:



From top the stack contains a sheet of heavy plywood, airbag, heavy ply, SIP (luan, blueboard, luan), heavy ply.

I am still considering how massive the frame needs to be. At 7 psi and with 1' centers the 4 foot spans carry a 4000 pound load, and each vertical in in 2000 pound of tension. I was trained as an Aeronautical Enginner over 30 years ago so I need to get some old text books out and see what kind of members are needed. We specialized in aluminum even back in those days! Wood is somewhat a mystery to me. Any help out there appreciated.

My only concern is keeping the plate beneath the sip flat too. This may need to be reinforced with cross braces too. I guess I could sandwich between two bags (above and below sip) as they only cost about 20-30 bucks each and would even out the pressure even if the plate below deforms slightly.

I will report back later but the vacuum bagging may actually be the most economical way to go.

Sam

[captainsam]

Dear Sam,
If you need 300 extra lbs of pressure let me know and I will drive over on one of my trips.

Guy

If you feet occupy 1 sq. ft. if area and... your wife weighs 420 lbs. and.... you can carry her on your shoulders..... and you know 31 other similar couples... bring them along... I think we have found the answer!

[Guy]

Dear Sam,

Would have taken more than four wives, so unless you have some "Stews" that qualify, we are going to have to keep our thinking caps on.

Here is a post from Rdoor: a fairly knowledgeable guy on Sipsweb.

Here's an update on building one off panels I've been working on. I finished the first 19 panels yesterday and I would say I'm pleased with the results. Simply put, I'm using a vacuum box, 2x8 sides, Formica bottom and a vinyl awning top sealed with 1 1/4" by 1/2" closed cell rubber weather strip covered with many coats of rubber paint to seal the tarp to the box. Vacuum is provided with a Shop Vac to create the initial seal and then switched over to a 10 CFM vacuum pump (Ebay - $200). I'm using Mor-Ad 646 for a number of reasons. It's a one part moisture activated product requiring 3 PSI vacuum with a work time of 10 minutes and pressure time of about 30 minutes which allow for adequate time to build and a decent level of production. I can build a panel every 45 minutes or so. I measure the adhesive with a digital scale (Wal Mart - $30) with a 2 gram accuracy which gets me very close to the 12 gm sq ft. I spread with a regular drywall trowel on the smooth side of the OSB and spray just before it goes into the box. Observations: It's very thick like cold honey, it does start to activate once it's exposed to air, I don't have access to dibasic ester yet so clean up is difficult (trowel only), once it gets on your hands and dries it DOESN'T come off. My hands look like I'm in the middle of a tear down of a diesel engine. Cost breakdown per sq ft is OSB $.84 ($13.50 sheet), EPS 5.5 in $.682 ($.124 bd ft), glue $.20 or about $1.72 sq ft. at todays prices for me. This is just a snapshot, prices have gone up dramatically recently due to oil (EPS up over 35%).
Given the opportunity to do it again, it would take MUCH less time to come up with a practical system and cheaper to build (not having to start over). I hope this helps.

[captainsam]

Dear Sam,

so unless you have some "Stews" that qualify

Guy

Well, we do have a few "wide bodies" that might qualify

Thanks for the info. I have been reading that forum on and off for a while. Mostly residential oriented, but losts of good info.

Sam

[critter]

hey all,
i goy a headache just from reading that and i graduated the 8th grade....... twice

[Mark Mckeeman]

Thanks for the math lesson Sam

Seriously though, you must be enjoying this exersise. Your engineering background was put to good use in that last post.

To my credit, the chap that Guy quoted seems to be using a method similar to what I described, granted you need a better vacuum source than a shop vac.

You may require 5-7 psi the make a text book SIP but is that really required to make a sufficient bond for a TD panel. Lets face it, lots of folks out there are camping in a stick framed foam core box that was sand bagged with a few nails added here and there and it's more than adequate.

As for glue, If it's as thick as honey and difficult to spread with a 10 minute work time, requires water to activate and toxic chemicals to clean-up and costs $20 a quart I don't want to use it. If the stuff I mentioned can hold down a High school gymnasium floor for 20 years it's good enough for me.



Critter, I think I was in your graduating class.....twice

[alaska teardrop]

edit-gone

[Guy]

What attracted me to that post is the psi required to bond for structural purposes, 3 psi instead of 5-7 psi. Gorilla glue costs much more than 20 dollars a quartand dibasic esters are considered by some to be non-hazardous, which I too disagree with wholeheartedly, especially since I am an Agent Orange baby.

[GPW]

Did anyone think to contact a SIP manufacturer , send them a drawing and get a quote ... probably cheaper than you think and already routed for the wiring ... crumbs for thought

[captainsam]

Thanks for the math lesson Sam

You may require 5-7 psi the make a text book SIP but is that really required to make a sufficient bond for a TD panel. Lets face it, lots of folks out there are camping in a stick framed foam core box that was sand bagged with a few nails added here and there and it's more than adequate. :

I agree that we are probably overbuilding.... that's my nature. I tend to add an extra safety margin... a product of 35+ years in the cockpit.

The SIP manufacturers are building things for other people that will have to last for more than 50 years. They have lawyers.

I told you in an earlier post I built a 5.2mm Luan faced 2" XPS foam cored panel with gorilla glue and some 5 gallon paint buckets as the only clamping and despite some edge gaps, I would say it is more than strong enough to build a teardrop. That is just a gut feeling but it held me! The panel below was 1' X 4' and flexed less than a solid wood 2 X 12.



I do think you can get away with a lot less pressure with the right adhesive. Next weekend, I am going to try another panel, this time with a shop vac as the pressure source. I would then like to load that panel and the earlier one to failure and see how much moment it can really take.

Sam

[Guy]

Dear Sam,

Here is a link that I posted about a year ago. It may be helpful or it may be useless. You be the judge.

http://www.oneoceankayaks.com/Sandcore.htm

[molethai]

Thank you Guy. I was following this thread with intrest, but not sure what all the fuss was. Now I see the light.

[alaska teardrop]

Thanks for that link Guy.

Explains why you can't bend a two sided panel of extruded polystyrene.

Here is a link to a Dow patent where they bend a one sided panel and then add the other.

www.freepatentsonline.com/4078959.html

Two more that might be of interest.

www.freepatentsonline.com/6899779.html? ... ht=4078959

www.panelprojects.com/laminatedpanels.htm

Fred

[captainsam]

Well this weekend I had a chance to continue my experimentation toward building a Structural Insulated Panel (SIP) which I will report on in a minute. I continue to look for a good source of pressure to press panels but am also looking to figure out how little pressure will suffice.

This week I spoke with a Mr. Tom Schwartz, of Rohm Hass, They are the makers of one of the two main adhesives used in commercial SIP production. I asked about their product, MorAd M-640. I found this product for about $300 for a 5 gallon bucket. PRICEY. They suggest an application of 12 gm/sq.ft. That means about 20-25 4 X 8 panels or about $12-15 a panel for the adhesive. This stuff is single part, water activated, can be applied with a roller, and has an open time of about 20 minutes. It needs to be applied and clamped by that time or you have an expensive mess on your hands.


I asked about pressures required because I had heard that MoAd used lower pressures than the other leading SIP adhesive, Iso Grip by Ashland Chemical. Not so. He said it is desirable to use as much pressure as possible short of crushing the core (foam). Of course his lawyer told him to say that. He explained that as the adhesive is activated, it foams (like gorilla glue) and out gasses. This gas tends to push the panel apart, creating a thicker bondline. Since their adhesive has no strength itself, this is a bad thing. It is good at glueing two surfaces together, but is a poor gap filler. He said that by using XPS foam like I have been, it requires a higher pressure than using the white EPS foam (beadboard) since it's looser structure is more porus and can absorb more of the out gassing.

I mentioned that I had been scuffing the foam surface with some 60 grit sand paper to take off the shine before applying the adhesive (gorilla glue). He said that "by chance" I was doing just the right thing as it also allows the out gassing to be absorbed more easily in the foam. He also warned that due to the variable nature of luan, the pore structure of some wood facing panels may also allow the gassing to be absorbed creating a good panel with a lower clamping pressure. Of course, the next batch of luan might have a very tight pore structure and not work nearly so well.

He seemed to agree that if reasonable precautions were taken in home "manufacturing" and a considerable safety margin was allowed in the design, that lower clamping pressures could build a pretty strong panel.

Yesterday I just couldn't wait to build another panel so even without a viable clamping press, I built another 1' X 4' test panel using the same luan and foam as before... but this time with another adhesive. I selected PL Premium Construction adhesive for several reasons:

1) It is readily available at Home Depot in bulk for about $5 for 30oz. large caulk gun tubes. That is a fraction of the cost of gorilla glue.

2) It is a water activated Polyurethane Adhesive like all other SIP adhesives.

3) It is easy to apply. I made a small notched trowel from a 8" Plastic Bondo spatula ( I cut many 1/8' notches) to spread the lines of adhesive I had put on the panel. Much easier than Gorilla glue!

4) The open time is 30 minutes... more than enough time to spread the adhesive on both sides of the foam.

5) It is advertised to have structural gap filling properties up to 3/8". I reasoned that of the bondline was not fully compressed due to a lower pressure, structural integrity would not be as easily lost.

6) I spoke with their tech rep and he said the adhesive would be great for this application( glue wood to foam), and require only enough pressure to keep the gaps closed between the foam and wood until it sets.

I think the reason such a glue is not used commercially to make sips is that it is labor intensive to spread (they want a spray on product). They also want quick curing glue so they can keep panel moving through their presses. I have all day.

Yesterday morning I built a panel and allowed it to cure 24 hours before loading it. The cure is said to take less than 8 hours with the strength continue to increases up to 3 days depending on weather.

I was very happy with the results:




I feel this was my best panel to date. I used three 60 lb. sand bags to clamp the panel during cure. I removed the bags after 6 hours. There was no sign of delamination around any edges and this was with only 0.3 psi clamping pressure! I still think I need more, but I am convinced that 1-2 psi will probably produce a panel strong enough for my teardrop needs.

I recruited my 15 year old ( 6'3 220+ lb) son to help "test" the panel.



Imagine trying that with a sheet of 3/4 in plywood. And this panel weighs less than a 1/2" sheet of plywood ( and has about R-11 insulation to boot).

I am now going to figure out the best way to easily and inexpensively deliver 1-2 psi to the panel and make a few more test articles. The lower requirement opens up a lot of clamping possibilities that I had discarded as impractical before.

I have a two gallons of two part expanding polyurethane foam arriving this next week. I want to build yet another 1' X 4' panel using that method. The advantage it offers is the ability to build curved panels quite easily... kind of nice for a tear.

After that panel is built I am going to try to load each panel to failure to see what kind of strength I really have.

The SIP saga continues!

Sam

[alaska teardrop]

Sam wrote: I have a two gallons of two part expanding polyurethane foam arriving this next week. I want to build yet another 1' X 4' panel using that method. The advantage it offers is the ability to build curved panels quite easily... kind of nice for a tear.

Sam - I think that you're really on to something here.

Keep up the good research.

Fred